There are two quite different approaches to deriving an electroacoustic theory. The first was suggested by Enderby and Booth 50 years ago and later modified by Marlow, Fairhurst and Pendse. The second was suggested by O'Brien about 10 years ago (O'Brien's approach). He introduced a special relationship between kinetic coefficients that is assumed to be valid in a concentrated system. This approach requires also a theory for dynamic electrophoretic mobility. The most recent version of this theory for concentrated systems was created by Ohshima, Shilov, and A. Dukhin on the basis of the cell model. A hybrid of the O'Brien relationship and this new electrophoretic mobility theory yields expressions for electroacoustic effects in the concentrated systems. We call it “hybrid O'Brien's theory”. In principle these two approaches must lead to the same result. To test this expectation, we should generalize the first approach such that it is valid for concentrates. We have done this using the Kuvabara cell model fo...